J. Agric. Food Chem. 2005, 53, 1495−1498
1495
Effect of Far-Infrared Irradiation on the Antioxidant Activity of
Defatted Sesame Meal Extracts
SEUNG-CHEOL LEE,*,† SEOK-MOON JEONG,† SO-YOUNG KIM,† K. C. NAM,‡
D. U. AHN‡
AND
Division of Food Science and Biotechnology, Kyungnam University, Masan 631-701, Korea, and
Department of Animal Science, Iowa State University, Ames, Iowa 50011-3150
To determine the effect of far-infrared (FIR) irradiation on the antioxidant activities of sesame meal,
half of sesame seeds were FIR-irradiated and then oil was extracted from the seeds. The resulting
defatted sesame meal (DSM) was extracted with methanol, and the antioxidant activities of methanolic
extract were determined. FIR irradiation of sesame seeds for 30 min increased the total phenol content
from 34.0 to 59.0 µM and radical scavenging activity of DSM extracts from 26.40 to 68.76%. The
induction time of lipid oxidation of oil added to extracts was also retarded from 0.82 to 0.96 h. According
to the gas chromatography-mass spectrometry analysis, several low molecular weight phenolic
compounds, such as p-hydroxy benzoic acid, vanillic acid, p-coumaric acid, isoferulic acid, and
o-coumaric acid, were frequently detected in FIR-irradiated DSM extracts as compared to unirradiated
ones. These results indicated that FIR irradiation of sesame seeds increased the antioxidant activity
of methanolic extracts of DSM.
KEYWORDS:
compounds
Defatted sesame meal extract; far-infrared irradiation; antioxidant activity; phenolic
INTRODUCTION
Sesame (Sesamum indicum L.) seed is one of the most
important oil seed crops in the world. Sesame seed is composed
of 45-50% lipid, 5-6% moisture, 10-15% carbohydrate,
5-6% ash, 4-5% fiber, and 15-20% protein. Sesame seed is
not only a good source for edible oil but is also widely used in
baked foods and confectionery products (1). Sesame oil is highly
resistant to oxidative changes during storage due to high
concentrations of various antioxidants in it. Sesame oil significantly decreased lipid peroxidation and serum nitrite levels and
attenuated cecal ligation and puncture-induced hepatic injury
in rats (2). In addition, compounds in sesame oil showed
anticarcinogenic (3), blood pressure lowering (4), and serum
lipid lowering effects (5, 6) in experimental animals and humans.
Defatted sesame meal (DSM) obtained from oil extraction is
either used as a feed ingredient for domestic animals or
composted. It has been reported that sesame oil extracted from
seeds with hulls is more stable than that from dehulled seeds
(7), indicating that antioxidant components may exist in the
sesame hull. Chang and others (8) reported that the sesame coat
has a significant antioxidant activity in various in vitro systems.
Feeding defatted sesame oil meal showed a hypocholesterolemic
effect in rabbits (9) and promoted the detoxifying capability of
ethanol-medicated rats (10).
* To whom correspondence should be addressed. Tel: + 82-55-2492684. Fax: 82-55-249-2995. E-mail: sclee@kyungnam.ac.kr.
† Kyungnam University.
‡ Iowa State University.
Antioxidants such as flavonoids, tannins, coumatins, curcuminoids, xanthons, phenolics, and terpenoids are found in
various plant products (e.g., fruits, leaves, seeds, and oils) (11).
For this reason, there is a growing interest in separating these
plant antioxidants and using them as natural antioxidants. Some
components from fruit and vegetable extracts showed as strong
antioxidant effects as synthetic antioxidants in model systems
(12). In general, the seed coat plays an important role in
protecting seeds from oxidative damage because the seed coat
possesses a large quantity of endogenous antioxidants such as
phenolic compounds (13, 14).
Many natural plant antioxidants, however, exist either as a
bound form to high molecular weight compounds or as a part
of repeating subunits of high molecular weight polymers. Several
methods including far-infrared (FIR) irradiation are known to
liberate and activate low molecular weight natural antioxidants
in plants (15). FIR rays are defined as electromagnetic waves,
which have wavelengths longer than 4 µm but shorter than
microwaves (λ > 0.1 cm). FIR rays are biologically active (16)
and transfer heat to the center of materials evenly without
degrading the constituent molecules on the surface. FIR,
however, may have the capability to cleave covalent bonds and
liberate antioxidant compounds such as flavonoids, carotene,
tannin, ascorbate, flavoprotein, or polyphenols from repeating
polymers (15, 17). Therefore, the objective of this research was
to elucidate the effect of FIR irradiation on the antioxidant
activities of extracts from DSM.
10.1021/jf048620x CCC: $30.25 © 2005 American Chemical Society
Published on Web 01/29/2005
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Lee et al.
Table 1. Effect of FIR Irradiation on TPCs, DPPH RSA, and Induction Time (IT) of Lipid Peroxidation of Methanol Extracts from DSMs
FIR irradiation time (min)
TPC (µM)
RSA (%)
IT (h)
a -hDifferent
0
10
33.98g
52.52e
26.40h
0.643b
63.26f
0.570b
20
30
40
50
60
90
120
SEM
47.07f
58.76d
68.05c
69.40c
72.85b
73.25b
79.74a
60.29g
0.573b
68.76e
0.623b
74.04d
0.720a
75.25c
0.757a
76.35b
0.777a
76.24b
0.791a
77.78a
0.793a
0.717
0.304
0.019
letters within a row are significantly different (P < 0.05), n ) 3.
MATERIALS AND METHODS
Materials. White sesame seeds (S. indicum L.) were purchased from
a local market in Masan, South Korea. 2-Thiobarbituric acid, tannic
acid, lard oil, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) were purchased
from Sigma Chemical Co. (St. Louis, MO). Folin-Ciocalteu reagent
was from Wako Pure Chemical Industries, Ltd. (Osaka, Japan).
FIR Irradiation onto Sesame Seed. Whole sesame seeds (20 g) in
a wooden box (50 cm × 40 cm × 40 cm) were irradiated using a FIR
heater (35 cm × 10 cm, output 300 W, Hakko Electric Machine Works
Co., Ltd., Nagano, Japan), which emitted radiation at the wavelength
range of 2 and 14 µm at 200 °C for 10, 20, 30, 40, 50, 60, 90, or 120
min. The sample holding tray in the middle of treating box was placed
to face a FIR heater in a parallel position, and the distance between
the sample and the heater was 5 cm. After irradiation, the seeds were
allowed to cool to ambient temperature before oil extraction.
Preparation of DSM and Its Methanolic Extract. The irradiated
sesame seeds (20 g) were crushed, and oil was extracted using an
electric oil extractor (model Do-9001; Donga Oscar Co., Gimhae,
Korea). The remaining oil in residue was extracted with 100 mL of
n-hexane by vigorous shaking in a three-cycle shaker, filtered through
Whatman no. 1 filter paper. The residue (DSM) was collected and dried
at room temperature.
The DSM (10 g) was extracted with 100 mL of methanol in a shaking
incubator overnight at room temperature and filtered through Whatman
no.1 filter paper. The residue was re-extracted under the same
conditions. The first and second extracts were pooled and filtered
through a Whatman nylon membrane filter (0.2 µm, Millipore filtration
kit MA 01730, Millipore Co., Bedford, England). The methanol in the
filtrate was evaporated under vacuum at 40 °C using a rotary evaporator
(model Eyela N-1000; Tokyo Rikakikai Co., Tokyo, Japan). The dried
methanolic extract of DSM was redissolved in methanol (1 mg/mL)
and used for further analyses.
Total Phenolic Content (TPC). The TPC of DSM extracts was
determined using a method described by Gutfinger (18). One milliliter
of DSM extract (1 mg/mL) was mixed with 1 mL of 50% FolinCiocalteu reagent and 1 mL of 2% Na2CO3 and centrifuged at 13400g
for 5 min. The absorbance at 750 nm was measured with a spectrophotometer (model UV-1601; Shimadzu, Tokyo, Japan) after 30 min
of incubation at room temperature. TPC was expressed as a tannic acid
equivalent.
Radical Scavenging Activity (RSA). The effect of extracts on DPPH
RSA was estimated using a method described by Blois (19). After
mixing 1 mL of 0.041 mM DPPH in ethanol with 0.2 mL of DSM
extract (1 mg/mL) for 10 min, the absorbance was measured at 517
nm. RSA was expressed as a percentage inhibition and was calculated
using the following formula:
% DPPH RSA ) (1 - sample OD/control OD) × 100
Rancimat Method. The peroxidation induction period of lard as
affected by the addition of antioxidant was determined according to
the method of Chen and Ho (20). A Metrohm 793 Rancimat instrument
(Herisan, Switzerland) was used to determine the oxidation of lard with
or without the addition of sesame meal extract. Oxidation was induced
at 120 °C with air at a flow rate of 20 L/h. One milliliter of each sample
(10 mg/mL) was added to lard (2.5 g) and then mixed vigorously with
vortex for 8 s immediately before starting the Rancimat measurement.
Composition of DSMs Extracts. Each DSM extract received either
unirradiation or 30 min of FIR irradiation and were dissolved in ethanol
(200 mg/mL) and centrifuged at 13400g for 5 min to precipitate
undissolved materials. The supernatant was mixed with 4 volumes of
BSA [N,O-bis(trimethylsilyl)acetamide] and derivatized in a water bath
(70 °C) for 15 min (21). The compounds in the DSM extract were
identified using gas chromatography/mass spectrometry (model GC6890/
MS5973; Hewlett-Packard Co., Wilmington, DE). A split inlet (99:1)
was used to inject samples (5 µL) into an HP-5 column (30 m, 0.32
mm i.d., 0.25 µm film; Hewlett-Packard Co.). A ramped oven
temperature was used (100 °C for 2 min, increased to 270 °C at 10
°C/min, and held for 6 min). The inlet temperature was 250 °C, and
the carrier gas was He at a constant flow of 1.5 mL/min. The ionization
potential of the mass selective detector was 70 eV, and the scan range
was 19.1-400 m/z. Identification of compounds was achieved by
comparing mass spectral data of samples with those of the Wiley library
(Hewlett-Packard Co.).
Statistical Analysis. All measurements were done in triplicate, and
the analysis of variance was conducted by the General Linear Model
procedure of SAS (SAS Institute) software (22). Student-NewmanKeul’s multiple range tests and t-tests were used to compare the
differences among mean values (P < 0.05).
RESULTS AND DISCUSSION
Effect of FIR Irradiation on the Antioxidant Activities of
DSM Extracts. The effects of FIR irradiation on the antioxidant
activities of DSM extracts were determined by TPC, RSA, and
induction time for lipid peroxidation. Phenolic compounds are
known to act as antioxidants not only because of their ability
to donate hydrogen or electrons but also because they form
stable radical intermediates (23, 24). The TPC in methanolic
extract of DSM increased significantly by FIR irradiation (Table
1). TPC in DSM increased from 34.0 µM in unirradiated control
to 59.0 µM with 30 min of FIR irradiation. The TPC increased
with the increase of FIR irradiation time but reached a plateau
after about 60 min of irradiation. The DPPH RSA of the DSM
extract also significantly increased with FIR irradiation (Table
1). After FIR irradiation for 30 min, the RSA of DSM extracts
increased from 26.40 to 68.76%. RSA also increased with
increasing FIR irradiation time and reached a plateau after about
60 min of irradiation in the TPC. The Rancimat method is
commonly used to evaluate the potency of various antioxidants
(25). The longer the induction period of lard, the stronger is
the antioxidant activity of the compound. The induction time
of lard increased from 0.82 to 0.96 h when sesame seeds were
FIR-irradiated for 60 min (Table 1).
Roasting conditions of sesame seeds affect the antioxidant
activity of sesame oil. Kim (26) reported that the storage stability
of unroasted sesame oil was low, but roasting of sesame seed
at 170 °C or higher significantly increased the stability of sesame
oil. The highest sesamol content and storage stability of sesame
oil was achieved when sesame seeds were roasted at 200-220
°C. Yoshida and Takagi (27) reported that sesamol, a potent
phenolic antioxidant, increased as the roasting temperature of
sesame seeds increased to 180 °C or higher. We also found
that roasting temperature and time of sesame seeds affected the
antioxidant activity of DSM significantly (28). Simple heating
increased the antioxidant activity of DSM (28) but not rice hull
(17). FIR irradiation cleaved and liberated phenolic compounds
Antioxidant Activity of Defatted Sesame Meals
J. Agric. Food Chem., Vol. 53, No. 5, 2005
1497
Table 2. Detected Phenolic Compounds in the Methanolic Extracts of
DSM from FIR-Irradiated and Nonirradiated Sesame Seeds
total ion counts × 104
compound
nonirradiated
FIR irradiated
p-hydroxy benzoic acida
o-coumaric acida
vanillic acida
p-coumaric acida
isoferulic acid
totala
483
0
4563
2371
3027
10444
2842
1233
8899
25286
3437
41697
a The t-test shows the significant difference between two samples (P < 0.05),
n ) 3.
the repeating subunits of high molecular weighted polymers (14,
19, 20). This study also showed that FIR irradiation of sesame
seeds helped liberate phenolic compounds from DSM and
increased the antioxidant activity of DMS extract. FIR irradiation
is simple and effective in releasing antioxidant compounds from
agricultural byproducts and is easy to scale-up for industrial
use.
LITERATURE CITED
Figure 1. Gas chromatograms of DSM extracts, unirradiated (A) and FIR
irradiated (B) at 200 °C for 30 min after BSA derivatization. The peaks
in panel A are as follows: 1, p-hydroxybenzoic acid; 2, vanillic acid; 3,
p-coumaric acid; and 4, isoferulic acid. The peaks in panel B are as
follows: 1, p-hydroxybenzoic acid; 2, o-coumaric acid; 3, vanillic acid; 4,
p-coumaric acid; and 5, isoferulic acid.
and increased the antioxidant activity of DSM and rice hull (17).
These results indicate that phenolic antioxidant compounds
present in several forms and effective processing steps for
liberating antioxidant compounds from plants should be different
depending upon plant species.
Identification of DSM Extracts. Phenolic compounds are
the most active antioxidant derivatives in plants (29). Generally,
the outer layers of a plant such as the peel, shell, and hull contain
large amounts of polyphenolic compounds to protect inner
materials. A number of phenolic acids are linked to various cell
wall components such as arabinoxylans and proteins (30). The
phenolic compounds in DMS were reported to contain 75.3%
soluble esters and 24.7% of insoluble residue form (31).
Several low molecular weight phenolic compounds such as
p-hydroxybenzoic acid, vanillic acid, p-coumaric acid, isoferulic
acid, and o-coumaric acid were detected in the methanolic
extracts of DSM (Figure 1). In addition to sesamol and
tocopherols, many other antioxidant compounds such as polyphenol compounds were present in sesame seeds and DSM (32).
Fenton and others (33) reported that polyphenol compounds such
as caffeic, p-coumaric, ferulic, p-hydroxybenzoic, sinapic, transcinnamic, and chlorogenic acids were present in the hydrolysate
of rapeseed meal. There are slight differences in the kinds of
phenolic compounds detected in unirradiated and FIR-irradiated
DSM extracts. However, the amounts of p-hydroxybenzoic acid,
vanillic acid, p-coumaric acid, and isoferulic acid were higher
in FIR-irradiated samples than the control, and o-coumaric acid
was newly detected (Table 2).
It was reported that FIR irradiation and/or fermentation of
plant increased antioxidant activity of its extract because those
treatments liberated low molecular antioxidant compounds from
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Received for review August 18, 2004. Revised manuscript received
December 3, 2004. Accepted December 16, 2004. This study was
supported by the Ministry of Science and Technology (MOST) and the
Korea Science and Engineering Foundation (KOSEF) through the
Coastal Resource and Environmental Research Center (CRERC) at
Kyungnam University (R12-1999-025-10001-0), Korea, and State of
Iowa Funds. S.-M.J. and S.-Y.K. received scholarships from the Brain
Korea 21 Program of the Korean Ministry of Education.
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